Myeloid differentiation factor 88 (MyD88) recruits signaling proteins to the intracellular domain of receptors belonging to the Toll-like/Interleukin-1 receptor (TIR) superfamily. MyD88 plays a crucial role in the transduction events triggered by all toll-like receptors (TLR), except TLR3, as well as the family of IL-1 receptors (such as the IL-1 receptor and IL-18 receptor). Therefore, inhibition of this adaptor protein, involved in the activation of NF-kB, triggered by signals from receptors that recognize distinct ligands but share the same transduction pathway, is expected to be more effective than inhibition of the individual ligand activities.
There is a consensus that MyD88-dependent signaling contributes to Experimental Autoimmune Encephalomyelitis (EAE), the animal model of multiple sclerosis (Socorro Miranda-Hernandez and Alan G Baxter, Am J Clin Exp Immunol. 2013; 2(1): 75-93). Mice lacking MyD88 are highly susceptible to infectious diseases, but they are for the most part resistant to experimentally-induced autoimmune diseases such as EAE. MyD88 deficient mice are not only resistant to EAE induced by active immunization against CNS antigens, but also to EAE induced by passive transfer of previously activated encephalitogenic wild-type (WT) T cells (Cohen et al., J Immunol., 2010, 184).
There is also evidence that activating mutations in MyD88 are common in subtypes of lymphoma. Furthermore, strong preclinical evidence suggests that MyD88 drives oncogenesis through inflammatory and non-inflammatory pathways (Salcedo et al, Trends in Immunology 2013 34(8):379-389; Ngo et al Nature 2011, 470:115-119, 3. Yang et al, Blood 2013 122(7):1222-1232).
The MyD88 function is dependent on homodimerization (MyD88-MyD88) and heterodimerization (MyD88-TLR, MyD88-cytokine receptor, or MyD88-kinase). Multiple MyD88 molecules then form a protein complex (termed the “Myddosome”) that is critical for recruitment of downstream kinases and their phosphorylation. The crystal structure of MyD88 TIR domain revealed a loop between the second beta strand and the second alpha helix (the “BB loop”) that mediates dimerization (Loiarrio et al., J. Biol Chem 2005, 280, 16, 15809-15814). The BB loop heptapeptide having the sequence RDVLPGT (SEQ ID NO: 1), that correlates to this region, competitively inhibits dimerization.
Several small molecule inhibitors of MyD88 are known. Bartfai et al., PNAS 2003, 100, 13, 7971-7976 reported a low molecular weight MyD88 mimetic, hydrocinnamoyl-L-valyl pyrrolidone, modeled on a tripeptide sequence of the BB-loop of the TIR domain. The compound interferes with the interaction between mouse MyD88 and IL-1RI.
Fanto et al., J. Med. Chem 2008, 51, 1189-1202 describe the design, synthesis and in-vitro activity of peptidomimetic inhibitors of MyD88 which also interfere with MyD88 dimerization. The small molecules described comprise a beta turn mimetic and an arginine mimetic connected by a spacer.
Olson et al., Nature (Scientific Reports 5, Article number: 14246, 2015), discovered small molecule inhibitors of MyD88-dependent signaling pathways using a computational screen. The best compounds inhibit cytokine secretion at micromolar range in human cells and protect mice from septic shock.
Van Tassell et al., J Cardiovasc Pharmacol. 2010 55(4):385-90 have showed that inhibition of MyD88 prevents left ventricular dilation and hypertrophy after experimental acute myocardial infarction in the mouse and suggests that MyD88 may be a viable target for pharmacologic inhibition in acute myocardial infarction.
US20080064643 discloses non-natural peptides and peptidomimetic of the 7 amino acids linear BB loop peptide.
Autoimmune diseases are characterized by over-abundant inflammation. Multiple sclerosis is an autoimmune inflammatory demyelinating disease of the central nervous system (CNS). MS affects mainly young adults and it is the leading cause of neurological disability in this age group. The course of the MS is either relapsing and remitting or progressive. During the relapses of the disease, autoimmune, anti-myelin reactive lymphocytes are produced, activated and recruited from the peripheral immune system, enter the CNS and attack the myelin components, inducing neurological deficits which depend on the area of the white matter of the CNS that is affected each time (i.e. loss of vision, motor paralysis, instability of gait, problems in coordination of movements, loss of sphincters control, sensory disturbances etc). Despite dramatic improvement during the last decades, in the diagnostic tools for MS (basically due to the widespread availability of brain and spinal MRI), understanding of the basic etiology of the disease remains limited. Fully effective control of the disease activity and progression and the repair of damaged myelin are key objectives for current and future investigators. Based on the widely accepted autoimmune pathogenetic model, the current treatment options for MS include various modalities that downregulate or modulate the inflammatory process and the immune anti-myelin responses. Acute attacks (relapses) of MS are typically treated with glucocorticoids. Patients with relapsing-remitting MS who have current disease activity manifested by clinical symptoms or active new MRI lesions are treated with other, long-term acting, immunomodulatory drugs, such as interferon beta (Avonex®, Rebif®, Betaseron®), glatiramer acetate (Copaxone®), fingolimod and the chemotherapeutic agent mitoxanthrone (Compston, A.; Coles, A., Multiple sclerosis. Lancet 2008, 372, (9648), 1502-17). Almost all of these drugs are administered with injections and are associated with various adverse effects which both limit their ease of use for long periods of time. In addition, all of these treatments are partially effective and can only reduce the relapse and progression rates of MS by approximately 30%.
Backbone cyclization (BC) was already proved to be a valuable tool in methodological conversion of active sites of proteins to cyclic peptides and even to small macrocycles (Hurevich et al., Bioorg Med Chem 2010, 18, (15), 5754-5761; Hayouka et al., Bioorg Med Chem 2010, 18, (23), 8388-8395; Hess et al., J Med Chem 2008, 51, (4), 1026-34). The BC method is used to introduce global constraints to active peptides. It differs from other cyclization methods since it utilizes non-natural building blocks for cycle anchors, mainly N-alkylated amino acids. BC proved superior to other stabilization methods since the resultant peptides had defined structures that led to better selectivity (Gazal et al., J Med Chem 2002, 45, (8), 1665-71; WO 99/65508) and improved pharmacological properties. The use of BC enables a combinatorial approach called “cycloscan”. It was used for generating and screening BC peptide libraries to find lead peptides that overlap with the bioactive conformation. In a cycloscan, all the peptides in the library bear the same sequence but differ from each other in other parameters that constraint the conformational space. Screening the library allows an iterative evaluation of the effect of chemical modifications on the structural properties and biological function. Changing the ring size and ring chemistry proved to be the most convenient modification to perform in cycloscan and has been used to synthesize small- and medium-sized peptide libraries. However, obtaining an active cyclic analog based on a linear sequence is not a straightforward process.
No cure exists for MS and there is a strong need for additional disease modifying therapies as many patients continue to worsen on currently available treatments. There is an unmet need for metabolically stable, tissue permeable, preferably orally bioavailable and more effective therapeutic modalities for MS.